In gas assisted injection molding, articles are produced by injecting molten plastic into the mold cavity and charging a body of pressurized gas or liquid therein to form a hollow portion in selected locations within the thermoplastic material. Pressure is maintained on the gas in the hollow space within the molded object until the plastic material in the mold cavity has set. Thereafter, the pressurized gas or liquid is released from the molded part""s hollow area, and the molded part is removed from the mold cavity.
Process limitations still exist in conventional gas assisted injection molding processes, which give less than the desired product properties and dimensions. One problem is a tendency of gas ribs located in the mold cavity to have areas that are not desirably hollowed out, since gas sometimes pushes molten plastic from opposing directions whereupon it is trapped and forms a block or slug of molding material. Such a region will not cool as fast as the rest of the adjacent hollow structure, which undercuts the product""s cycle time, and produces localized distortions and surface shrinkage. Another problem results when upon removal of the molded part, residual pressurized gas, trapped in the molded part, releases and causes wall eruptions at locations that are insufficiently cooled or have very thin walls. Still yet another problem is the interior of the gas channel remains hot long after the exterior surface cools. When exhausting gas back through the hot, viscous interior, the gas port or other point of exhaustion typically becomes obstructed.
Consequently, there exists a need to enhance cooling of molding material to prevent defects in molded articles, and reduce cycle times for manufacturing molded articles.
The present disclosure relates to gas assisted injection molding and, more particularly, to circulating fluid in gas channels within a molding material in a mold.
Disclosed is an apparatus and a method for manufacturing a molded article. The method comprises injecting a quantity of molding material sufficient for the preparation of the molded article into a cavity of a mold, injecting a first portion of fluid into the mold cavity, creating a gas channel within the molding material, and forming the molded article within the mold cavity. At least a portion of the first portion of fluid is exhausted through a gas port, a second portion of fluid is injected into the mold material, and the molded article is cooled within the mold cavity to a temperature beneath a softening point of the molding material.
The foregoing and other features and advantages will become more apparent from the following description of the best mode and accompanying drawings.
For a further understanding of the nature of the injection molding system and method of using the same, as well as other features and advantages thereof, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, which are meant to be exemplary, not limiting, and wherein like elements are numbered alike in the several figures.
FIG. 1 is a cross-sectional view of an embodiment of an injection nozzle assembly fitted within a mold of an injection molding system.
FIG. 2 is a partial cross-sectional view of the injection nozzle assembly of FIG. 1 and an embodiment of a pair of gas ports mounted on either side of the assembly within the mold cavity.